Mounting a sensor chip to a substrate is required for electrically connecting the sensor chip to other components. In case that the sensor chip comprises a sensing element for sensing a parameter of a fluid, the fluid needs to access the sensing element. And third, the sensor chip is desired to be mechanically protected. However, objectives as to the arrangement of a sensor chip on a substrate may be conflicting: For example, in terms of measurement quality, and in particular in terms of response time, it may be preferred to expose the sensor chip as such to the environment and thereby granting immediate access to the fluid. Such arrangement on the other hand does promote mechanical protection of the sensor chip. An arrangement of the sensor chip in a housing may on the other hand provide a sufficient mechanical protection, however, is detrimental as to the response time since the fluid to be measured needs to travel through the housing before reaching the sensor chip.
A housing or other hard plastic protection means requires several parts to be assembled, possibly in different production processes and with demanding tolerances for providing a sufficient sealing. A rubber cap in turn would not require tight tolerances in assembly, but increases the response time of the sensor chip drastically.
In addition, it was observed by the present inventors, that many materials used for a housing or a cap, such as hard plastics or rubber, contaminate the fluid to be measured. For example, in case the fluid being a gas and the sensing element being sensitive to an analyte the quantity of which analyte is desired to be determined in the gas, the gas supplied from the outside into the housing may be contaminated by the material of the housing outgassing and impacting the fluid in its chemical composition. It was also observed that in some instances the housing rather acts as a storage for portions of the fluid, or analytes thereof: For example, in the case of humidity sensing, the housing may absorb humidity from the fluid entering the housing and thereby falsifying the measurement result, too.